Process for preparing metal articles



Patented May 29, 1934 retires PATENT BFFICE 1,960,895 rnocnss non PREPARING METAL ARTICLES Willis H. Oastner, Cornwall, P a., assignor to Bethlehem Steel Company, a corporation of Pennsylvania No Drawing. Application February 21, 1930,

Serial No. 430,449

2 Claims. (o1. 148-4) My invention relates to a process for preparing metal articles which are to be of definite, predetermined shape or dimensions.

My invention relates to methods wherein the metal articles are to be subjected after their formation to a. heat operation at such temperatures as would normally oxidize the metal.

My invention consists in forming the article, coating with a nonoxidizable metal, and then heat treating at temperatures which would oxidize the article but for the protectivecoating.

My invention can probably be'best illustrated by giving a specific example. Obviously the protection sought is not to be limited to this specific illustration. As such example, let us take the manufacture of threaded bodies such as screws or bolts.

A ferrous metal blank is prepared of the desired form and dimensions and is then machined to produce threads of the desired character and dimensions. These screws, or at least the threaded portions thereof, are then placed in an electrolyte containing a chromium salt and electro plated to cover the threaded portions or such portions of the screw as it is desired to protect, with a very thin coating of chromium say of a thickness of from two to three ten-thousandths of an inch.

The screws are then subjected to a heat treatment to improve the mechanical characteristics of the -metal of such screws. They are heated above the critical range and quenched in oil, water or other suitable quenching medium. The screws are then drawn, that is they are held at an elevated temperature but such temperature as is below the critical range until the desired microstructure in the screw is obtained Such a treatment, if it were not for the chromium coating, would inevitably result in a more or less deep oxidation of the metal of the screw; For the threaded portion of the screw this would be especially detrimental as such oxidation would not only alter the fit of the screw because of the change in form and dimension, but the scale which might burn fast to the metal The chromium lit would be very troublesome. coating, which is sufiiciently thin not to substantially alter the desired-thread form and dimension, efiectively prevents any substantial oxida-' tion,

The chromium plating may be effected by any of the well known processes of the art.

While I have specified chromium and while chromium is especially advantageous, it is obvious that my invention contemplates the use.

of any protective material which will resist oxidation. 7 I

Obviously the protective coating must either be so thin as to be negligible so far as in its effects upon size and dimensions of the body being treated, or 'an allowance must be made for the thickness of the coating in the formation of the body prior to the coating.

By the expression heat treatment in the claims I intend to include any treatment at such temperatures as would cause oxidation of the metal of which the body is composed. For example, in addition to heating for hardening or for drawing, as above given operations such as normalizing. and the like obviously are also to be effectively included.

.ing before the heat treatment so that such heat treatment will have practically no effects upon the definite, predetermined form and dimensions desired in the article.

Having thus described my invention what I claim and desire to secure by Letters Patent is:

1. In a process for preparing ferrous articles to'have definite, predetermined form and dimensions, the steps of machining the article to the desired finished form and dimensions, covering with a coating of chromium of negligible thickness and heat treating at temperatures and under conditions which would oxidize the surface of the article but for the chromium coating.

2. In a process for manufacturing threaded articles to have threads of definite, predetermined form and dimensions, the steps of giving the article threads of the desired finished form and dimensions by machining, coating the threaded portion of the article with a coating of chromium sufliciently thin to inappreciably affect the form and dimensions of the thread and heat treating the articles at temperatures and under conditions which would oxidize the threads but. for the chromium coating.

. WILLIS H. CAS'INER. 

